Durable Laptop Batteries
EEVblog #140 – Battery Capacity Tutorial
Ever wanted to know what battery capacity is? Dave takes you through everything you need to know about amp-hours, mAh, watt hours, internal or series resistance, temperature effects, battery cutoff voltages, and characteristic curves. Part 2 coming soon.
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I am astounded by ur awesomeness… Keep up ur awesome videos and I hope u win the iinet top geek award
@luppa79 True battery capacity is measured in Wh
@tupham81 You don’t, and they aren’t. You have to read the datasheets. If thee data is not on their then you have to measure it yourself.
WRITTEN MAN, WRITTEN :p
So how do we know that different battery manufacturers are being fair and going by the same constant current/voltages for their mAh capacities?
In other words, how can I know that a no-name branded battery that claims to be 2800mAh is equivalent to an energizer? It would definitely explain why the cheapo ones I bought off eBay didnt last very long when the energizer niMh batteries last much longer.
Also how do we know what the capacity is after n amount of charge cycles?
You’re saying that the mAh definition assumes a certain voltage, but you’re making that assumption yourself. You would need to assume some voltage level if you want to calculate energy with a simple multiplication, but that’s not the fault of the definition of Ah. Neither does it call for keeping the current constant. For example, 1h of 200mA + 1h of 400mA usage equals 600mAh, no matter what the voltages are.
What is capacity? Does that mean energy or Ah capacity or something else? I don’t know.
@EEVblog Actually we both go it wrong! From wikipedia it’s 1J=1 W . s =1 W .h / 3600. So it’s
1J=1 W . s = 2.7778×10^(?4) W.h .
Multiplying all part with 3600 we have: 3600J=3600 W.s=1 W.h which is quite logic if you think that 3600sec=1h.
So 1.4 W.h is 1.4*3600J=5040J and 2.5W.h=2.5*3600J=9000J.
Think about this: an average person needs around 9000 kJ a day (not talking about manual labor or athletes here; they can easily use tripple the amount). That’s equivalent to the energy stored in 1000 AA batteries or a cube a little larger than 21x21x21cm³ stuffed with batteries. Running a human on batteries wouldn’t be cheap
. And if you have rechargeables: even with those 4x15min quick chargers you’d need 3 of these charges stuffed 24/7 to have enough energy.
@ReefMimic I’m giving you the information so you can work it out for yourself. You’re welcome.
Great educative Video! There is a little mistake at the Joule conversion equation 6:43 .
It’s 1J=1 W . s *3600=1 W .h
save me 28 mins next time and just tell us the best ones to get
@Certifiedfunds They will have a lower self discharge rate when colder, and hence a longer shelf life in theory.
@kd5gua It depends entirely on how you define the battery capacity and it’s end use into a particular load type. By the very definition, mAh or Wh capacities are implying a constant current or power discharge rate.
Thank you for the video Dave, very interesting! I’m also studying electrical engineering, but not in english. And I’m always having problems understanding what the ‘load’ is you are always talking about. Is it the current your circuit has to create, or is it the resistance it sees?
would it be posibal to make labscope from microphone?
Battery Capacity is important because of land fill issues. The quicker a Battery loses power the quicker it will end up in a land-fill.
@Certifiedfunds I think because it slows the chemical reactions that are responsible for capacity breakdown. All the internals corrode over time, the battery internally ‘leaks’, etc. By cooling it, you slow that process.
By how much, at what temperatures and for what durations, I haven’t a clue, so who knows if it’s effective. I just know thats how I reasoned it, hahaha.
I have two mini fridges in my garage, one for beer, and one for batteries and chemicals (epoxies and resins mostly)
Great tutorial! I used to work at a hobby shop, battery stuff for RC applications is the most misunderstood concept out there, even more so than how a 2-stroke glow engine works! hehe.
@Afrotechmods I am sorry but what does calculus has to do with my question. The integral of v with repsect to time, gives a unit of v.s which is not a unit of energy. The thing that I was missing is the fact that constant current is assumed.
@dosmaster88 I yeah I see, I forget about that. Of course. That’s the same reasoning behind putting battery capacity in Ah or mAh, assuming constant voltage throughout the battery’s life cycle. Correct?
veri technical, do it for dummies next time!
@Certifiedfunds yeah, I’ve done this but often wondered why myself.
GRAET TUTORIAL
Why do some people store batteries in the fridge?
@detectiveinspekta AA’s will have more capacity than a 9V battery, AAA’s it might be a toss up. But you’d have to do some ballpark calcs.